AbstractOur understanding of the effects of plant biodiversity on ecosystem function rests in large part on experiments that have disentangled environmental variables from local diversity. Yet phylogenetic diversity (PD) effects can be confounded by phylogenetic identity effects in such experiments if assemblages with low or high PD tend to be dominated by a single clade. We illustrate this problem in a 127-species experiment designed to test the effects of angiosperm PD and trait diversity on tallgrass prairie restoration outcomes. In this experiment, the taxon pool exhibits a phylogenetic bias: if species were randomly assigned to experimental assemblages, low PD plots would frequently be dominated by a single clade (the sunflower or daisy family, Asteraceae). We present a visualization tool for examining phylogenetic experiments for this bias and propose a taxonomically constrained experimental design to reduce the most egregious causes of bias. We then present the experimental design we developed using the constrained approach and summarize initial findings from this large-scale restoration experiment. Entanglement of phylogenetic diversity and phylogenetic identity is an underappreciated and likely widespread challenge for PD experiments, particularly those that draw upon a large number of candidate species. By recognizing, quantifying, and counteracting this bias, researchers can better differentiate the effects of PD per se from phylogenetic identity effects.
Alternate TitleChapter: Effects of Phylogenetic Diversity and Phylogenetic Identity in a Restoration Ecology Experiment